The present invention relates to a screw and a driver bit applied thereto, and to a combination of a screw and driver bit/wrench which realizes a tight engagement between an angular hole formed, for example, on a head of a hexagonal recessed screw or bolt and a driver bit provided with a bit tip formed to fit this angular hole, and which is capable of promptly and positively achieving attachment and detachment of the screw or the like by appropriate torque transmission.
FIGS. 13 to 16 show constructions of known conventional combinations of hexagonal recessed bolts and driver bits. FIGS. 13 and 14 show a conventional bolt having a hexagonal recess at the center of the bolt head. FIG. 15 illustrates a driver bit for the hexagonal recessed bolt. FIG. 16 depicts how the bolt and the driver bit are engaged.
A conventional bolt 10 shown in FIGS. 13 and 14 is provided with a hexagonal hole 12 at a bolt head 10a. This hexagonal hole 12 is formed so that constant, vertical wall surfaces 13 are respectively formed from the rim-edge toward a bolt neck 10b, and also a substantially conical bottom 14 with a slight slope is formed at the bottom thereof.
On the other hand, a conventional driver bit or wrench 20 in FIG. 15 is constructed to be provided with a hexagonal tip blade 22 which fits the hexagonal hole 12 of the above-mentioned bolt 10, and an appropriately elongated extended blade 22a formed to adapt to the shape of the vertical wall surfaces 13 formed from the rim-edge of the aforesaid hexagonal hole 12 toward the bolt neck 10b. The reference numeral 23 indicates a vertical wall formed on the side face between the above-mentioned tip blade 22 and the extended blade 22a. Namely, it is constructed so that the vertical wall 23 formed on the driver bit or wrench 20 tightly abuts and engages the vertical wall surface 13 formed on the hexagonal hole 12 of the above-described bolt 10.
According to a combination of the conventional bolt and driver bit thus constructed, when the bolt 10 and the driver bit 20 are engaged as shown in FIG. 16, for example, the tip blade 22 and extended blade 22a of the driver bit 20 will respectively fit to the vertical wall surfaces 13 of the hexagonal hole 12; and when the vertical wall 23 of the above-mentioned tip blade 22 and extended blade 22a abuts the vertical wall surface 13 on the hexagonal hole 12 in bolt 10 and the driver bit 20 is rotated, a specified torque can be transmitted to the bolt 10. In other words, it is possible to attach/detach a bolt to/from an object to be bolted.
According to the conventional combination of bolt 10 and driver bit 20 with the configuration as mentioned above, a hexagonal hole 12 in bolt head 10a forms constant, vertical wall surfaces 13 from its opening edge toward the bolt neck 10b. On the other hand, in the driver bit 20 corresponding thereto, an area which is adjacent to each ridgeline from the hexagonal tip blade 22 to the extended blade 22a forms the vertical wall 23 corresponding to the shape of the vertical wall surface 13 on the above-mentioned hexagonal hole 12, as shown in FIG. 16.
Accordingly, in order to fit the blade 22, 22a of driver bit 20 which has the above-mentioned vertical wall 23 forming the hexagonal side-surfaces, to the hexagonal hole 12 in bolt 10 which has the above-mentioned vertical wall side 13 forming the hexagonal side-surfaces, the tip blades 22 of the above-mentioned driver bit 20 is abutted to the opening edge of the hexagonal hole 12 in the above-mentioned bolt 10. However, since length L1, i.e., the length between the symmetrically-opposing ridgelines across the center of hexagonal hole 12, greatly differs from length L2, i.e., the length between vertical wall sides 13, it becomes very difficult to manually match the center of the hexagonal hole 12 in bolt 10 with the center of the tip blade 22 of driver bit 20. (See FIG. 14 (dashed line therein) and FIG. 16.)
In this case, accordingly, if a part of the tip blade 22 of driver bit 20 engagingly abuts a part of the opening edge of the hexagonal hole 12 in the above-mentioned bolt 10, a xe2x80x9ccome-outxe2x80x9d phenomenon, where the tip blade 22 of the above-mentioned driver bit 20 slips out of the opening edge of the hexagonal hole 12 in the above-mentioned bolt 10, may easily occur. When an excess force is applied to the driver bit 20, and when the torque resistance is large, each of the ridgeline portions at the opening edge of the hexagonal hole 12 will gradually be damaged, as illustrated with shaded portion 15 in FIG. 14. If this broken portion (shaded portion 15) gradually expands, the above-described come-out phenomenon of the driver bit 20 will occur frequently, finally making a screwing operation impossible.
From this view point, prevention of the come-out phenomenon for the above-mentioned driver bit 20 requires application of a large pressure against the hexagonal hole 12 when rotating the driver bit 20. No problem will occur when a rigid body, such as metal, is to be bolted or screwed. However, when handling precision parts, if the driver bit 20 comes out of the hexagonal hole 12, there occurs a disadvantageous effect of damage or breaking these precision parts.
Further, occurrence of the above-mentioned come-out phenomenon will accelerate wearing of the bit tip, i.e., tip blade 22 and extended blade 22a. Wearing at these sites will further promote occurrence of the above-mentioned come-out phenomenon. As a result, damages of the hexagonal hole will also increase.
Yet further, it is possible to prevent the come-out phenomenon by applying an excess pressure to the above-mentioned driver bit 20. However, it will be impossible to transmit a precise torque to a bolt, screw, or the like. Also, the amount of pressure applied to the driver bit 20 depends on an operator, resulting in a problem in that the screwing-torque applied to the bolt, screw or the like will vary.
When a bolt or screw is tightened manually, the operation of rotating the driver bit 20 by fully pressing the same against a bolt or screw may be a considerable labor and fatigue to the operator.
According to the conventional combination of bolt 10 and driver bit 20 as mentioned above, especially when an electrical tool is used to fix the screws, upon fitting the hexagonal hole to the bit tip, it is difficult to rotate a bolt while maintaining the bolt axis and the driver bit axis coaxially. When there is a deviation or slant between the bolt axis and the driver bit axis, for example, it is difficult to instantly fit the bit tip of driver bit 20 into the hexagonal hole at the bolt head as shown in FIG. 14 (dashed line therein) and FIG. 16, not only will the above-mentioned come-out phenomenon be caused frequently, but damage of the opening edge of hexagonal hole will also be frequently caused.
When a hexagonal recessed screw is to be detached, the same come-out phenomenon and damage of the opening edge of hexagonal hole may easily occur. In this case, the screw cannot be detached, resulting in such a situation where a part of the object having been screwed has to be destroyed. Such a situation is especially remarkable when dust or the like is filled into the hexagonal hole.
It is an object of the present invention to provide a combination of a screw and a driver bit or wrench capable of: effectively preventing the come-out phenomenon of the driver bit, preventing screws from being damaged which had occurred conventionally, always achieving a proper and prompt screwing operation even if the polygonal hole in the screw is broken, and remarkably improving operation efficiency, by improving the configuration of a polygonal hole in a screw head in a combination of a screw and a driver bit.
In order to achieve the above aims, the screw according to the present invention is a polygonal recessed screw comprising a polygonal recess having a substantially vertical wall surface with a predetermined depth in the central portion of a screw head thereof, and a conical bottom being formed from a lower edge portion of the vertical wall surface towards the central portion of a screw neck; characterized in providing, at the lower edge portion of the vertical wall surface of the polygonal recess formed in said screw head, a vertical stepped portion forming an inscribed circle of the polygon, and forming the conical bottom towards the central portion of the screw neck from the lower edge portion of the vertical stepped portion.
In this case, the polygonal recessed screw can either be constructed by a hexagonal recessed bolt, hexagonal recessed screw, a deformed hexagonal recessed bolt, a deformed hexagonal recessed screw, or other polygonal recessed or deformed polygonal recessed bolts or screws.
Further, a driver bit or a wrench which adapts to the above-described screw according to the present invention is characterized in forming a cylindrical protrusion forming an inscribed circle of a polygon at a tip end of a polygonal tip blade; forming the tip end surface of the cylindrical protrusion into a conical protrusion; and providing an extended blade forming a vertical wall vertically extending from said tip blade.
In this case, the driver bit or the wrench can have its cylindrical protrusion, formed on the tip blade, constructed to have a parallel cylindrical shape forming the inscribed circle of polygon.
Further, the cylindrical protrusion, formed on the tip blade, can be constructed to have, in its side surface at the tip edge forming the inscribed circle of polygon, a curved or a linear cylindrical shape.
Furthermore, a slit with a predetermined length extending in the bit-axis direction from its tip end surface can be constructed in one portion of the cylindrical protrusion formed on the tip blade.